JPS61236679A - Preparation of single crystal ferrite sphere - Google Patents

Abstract

PURPOSE:To prepare single crystal of ferrite easily by arranging polycrystalline ferrite sphere which have been formed previously to spherical form on a flat plate consisting of single crystal ferrite having a same crystal structure with the spherical ferrite and keeping the polycrystalline ferrite spheres at a temp. below the temp. where discontinuous growth of crystal particles is caused. CONSTITUTION:Polycrystalline ferrite is formed to spherical formed bodies or spherical sintered bodies. The polycrystalline ferrite bodies are arranged on a flat plate of single crystal ferrite having the same or almost same crystal structure as the polycrystalline ferrite to contact with the flat plate, and the polycrystalline ferrite spheres are held by heating at below a temp. where discontinuous growth of crystal particles of the polycrystalline ferrite is caused. By this method, growth of the spherical polycrystalline ferrite to spherical single crystal ferrite is caused.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing single crystal ferrite spheres.

(Prior art) Conventionally, when manufacturing single crystal ferrite spheres, a bulk single crystal is first created, then cut into rectangular parallelepipeds, and then polished into a spherical shape. There are methods such as , 2-pipe method, and bond method. In reality, these methods have been combined and a great deal of effort and time has been spent to polish the balls.

Methods for producing single crystal ferrite include methods in which a raw material is brought to a high temperature above its melting point to form a liquid phase and then cooled, such as the Bridgeman method, flux method, Czochralski method, and zone melting method. With this conventional method of obtaining a single crystal from a liquid phase at a high temperature above the melting point, it is difficult to make the shape of the obtained single crystal into a certain spherical shape. , a single crystal was obtained.

(Problems to be Solved by the Invention) Conventional methods require high temperatures of 1,600°C or higher to obtain large bulk single crystals, require expensive, complicated, and large manufacturing equipment, and Because it is difficult to accurately control the heating conditions during manufacturing, it has poor productivity, and requires processing steps such as cutting from bulk crystals and polishing balls, which takes a lot of man-hours and requires cutting into cubic shapes. In order to obtain a spherical n1 crystal from a bulk single crystal, more than half of the volume of the bulk ridge crystal is removed by machining due to the margin and the polishing margin from a cubic shape to a spherical shape.
The drawbacks were that the efficiency was extremely low and the resulting single-crystal taste was extremely expensive.

(Means for Solving the Problems) The present invention solves the drawbacks listed in -, and provides a spherical molded body or a spherical sintered body of polycrystalline ferrite having the same crystal structure as the polycrystalline ferrite. The spherical shape is formed by placing the plate in point contact with the single crystal plate and heating it at a temperature lower than the temperature at which discontinuous grain growth of the polycrystalline ferrite occurs and higher than the growth start temperature of the single crystal ferrite. A single crystal is grown from a point contact between a sintered body or a spherical sintered body and a 41 crystal plate to obtain a single crystal ferrite sphere.

(Function) When a polycrystalline ferrite body consisting of fine crystal grains is heated at a certain temperature below the melting point of the ferrite, the crystal grains constituting the polycrystalline ferrite body grow, and the crystal grains of this polycrystalline ferrite body grow. The higher the heating temperature, the faster the speed. Here, in the case of most polycrystalline ferrite bodies, the heating temperature is a certain constant temperature (varies depending on the composition, crystal system, manufacturing conditions, etc. of the polycrystalline ferrite body) as shown in Figure 1. : If the above is the case, a small part of the particles in the particle group during sintering will merge with the surrounding crystal group and grow into one large crystal, and once one particle grows into a larger particle than the surrounding particles. It then grows at a faster rate than its surroundings, and this continues, resulting in discontinuous grain growth.

In the present invention, a polycrystalline ferrite sphere previously formed into a spherical shape is placed in contact with a single crystal ferrite flat plate having the same or substantially the same crystal structure as the polycrystalline ferrite sphere, and then Ferrite 1 - By heating and maintaining the sphere at a temperature below Tb''C, which is the heating temperature at which discontinuous crystal grain growth occurs, the portion of the polycrystalline ferrite sphere that contacts the m-crystal ferrite body plate has larger crystal grains than the surrounding crystal grains. A single-crystal ferrite body is produced by growing particles with the same crystal plane direction as the low-crystal ferrite body, and using these particles as nuclei to cause discontinuous crystal grain growth throughout the polycrystalline ferrite sphere. .

In addition, the polycrystalline ferrite sphere used in the present invention has a small particle size because the particles that form the nucleus of discontinuous crystal grain growth formed at the contact point with the single crystal ferrite flat plate grow smoothly at a high speed. It is desirable that there are few impurities and almost no pores. In other words, the smaller the grain size, the more the number of sides of the core grain, the curvature of each side increases, and the greater the driving force that moves the grain boundary of the core grain toward the surrounding polycrystalline body. . In addition, since impurities and pores have the effect of pinning grain boundaries when they move, it is easier for grain boundaries to move when there are fewer impurities and pores. Polycrystalline ferrite spheres can also be obtained by processing a bulk polycrystalline sintered body, but before firing, a spherical molded body is produced by a conventional powder compaction method, etc., and then fired. You can also get it. In addition, there is a process in which a molded body is placed from the beginning as a spherical polycrystalline ferrite body placed on a single crystal ferrite body flat plate, and the molded body is fired to obtain a polycrystalline ferrite fired body. The process of manufacturing a crystalline ferrite body can be performed continuously.

In other words, in the conventional method for manufacturing bonded single crystals, the surface used for the bonding surface between polycrystalline ferrite and single crystal ferrite is S
After lapping with iC abrasive grains or the like, finishing to a mirror surface with diamond abrasive grains or the like, bonding, and further bonding treatment such as heat treatment was required. However, in the method for manufacturing spherical single-crystal ferrite according to the present invention, since the single-crystal ferrite and polycrystalline ferrite are joined at a point, there is no need to perform such a joining process. Further, the single crystal ferrite plate used in the present invention does not need to have the same composition as the spherical single crystal to be manufactured, nor does it need to have the same crystal lattice constant and coefficient of thermal expansion. In other words, in the conventional method for manufacturing a bonded single crystal, the bond between the polycrystalline ferrant and the single crystal ferrite is on the plane C, as shown in the cross-sectional view of FIG. By bonding with single crystal ferrite 1~, the lattice constant of part B, where the part that was originally polycrystalline ferrite has become qt crystallized,
If the coefficients of thermal expansion are different, strain will occur between A and B, causing cracks in the Qt crystal after cooling, and lattice defects will occur, making it difficult to obtain a high-quality single crystal. On the other hand, in the manufacturing method according to the present invention, the single crystal ferrite plate may be of a different composition system. However, it is preferable that the components contained in the Qi crystal ferrite plate do not include substances that diffuse into the spherical polycrystalline ferrite.

(Example) Example 1 Using yttrium oxide with a purity of 99.9% and ferric oxide with a purity of 99.5%, Y2O3 was 37.5m o ]%
, a mixture containing 62.5 m o ]% of Fe2O3 was prepared.

Experiments have revealed that discontinuous grain growth occurs in this mixture when it is heated and maintained at temperatures above 1490°C.

This mixture was molded to a diameter of 2 mm, this spherical molded body was produced, and the mixture was heated to 1400°C in an oxygen atmosphere of 98% or more.
Heating temperature increased at a rate of 0℃/hr, and then further raised to 1400℃
After heating and holding for 6 hours, the mixture was cooled at a rate of 200° C./hr to obtain a spherical polycrystal. Thereafter, the obtained spherical polycrystalline body was placed on a YIG single crystal thin plate, heated again at a rate of 200°C/hr to 1400°C in an oxygen atmosphere of 98% or more, and further heated from 1400°C to 1470°C. ℃ up to 10
It was heated to 4 degrees Celsius/hour and then cooled at a rate of 100 degrees Celsius/hr, yielding YTG single-crystalline bones.

Example 2 Using 99.9% pure yttrium oxide, 99.5% pure ferric oxide, and 99.6% pure aluminum oxide, Y2O3 was 37.5 m o 1%, Fe2O3 was 50 m
．． 0m.

A mixture of 1% AI, 03 and 12.5 m o 1% was prepared. Experiments have revealed that discontinuous grain growth occurs in this mixture when it is heated and held at 1490° C. or higher. This mixture was molded to a diameter of 2 mm to produce a spherical molded body, and heated to 140% in an oxygen atmosphere of 98% or more.
The temperature was raised to 0°C at a rate of 200°C/hr, and the temperature was further maintained at 1420°C for 6 hours, followed by cooling at a rate of 200°C/hr to obtain a spherical polycrystalline sintered body. Thereafter, the obtained polycrystalline sintered body was converted into gadolinium gallium garnet qt
The crystal thin plate was heated again at a rate of 200°C/hr to 1420°C in an oxygen atmosphere of 98% or more, and further heated at a rate of 5°C/hr from 1420°C to 1470°C. After that, the Al was cooled at a rate of 100°C/hr.
Substituted YIG single crystal spheres could be obtained.

Practical example 3 Using 99.9% pure yttrium oxide and 99.5% pure ferric oxide, Y2O3 is 37.5m o 1%
.

A mixture containing 62.5 m o ]% of Fe2O was prepared. Experiments have revealed that discontinuous grain growth occurs in this mixture when it is heated and held at 1490° C. or higher. This mixture was molded to a diameter of 2 mm to produce a spherical molded body, and then the spherical molded body was placed on a gadolinium gallium garnet heavy viscous thin plate, and the mixture was heated to 1400°C at a temperature of 20θ°C in an oxygen atmosphere of 98% or higher. It is possible to obtain YIG single crystal spheres by heating at a rate of 1,400°C to 1,470°C, then heating and sealing at a rate of 10°C/hr, and then cooling at a rate of 100°C/hr. did it.

(Effects of the Invention) The present invention is capable of obtaining single crystal spheres of ferrite by a simple method, greatly reducing the number of man-hours, and producing inexpensive single crystal spheres, which is extremely useful for industry. It is.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the relationship between the heating temperature and average particle diameter of polycrystals, and Figure 2 is an explanatory diagram showing the relationship between heating temperature and average particle size of polycrystals, and Figure 2 is an illustration of the relationship between a single crystal and a polycrystal, and a single crystal is grown in the polycrystal by bringing the single crystal into surface contact with the polycrystal. FIG.

Claims (1)

[Claims] A method for producing single-crystal ferrite in which polycrystalline ferrite and single-crystal ferrite are brought into contact and heated at a temperature lower than the temperature at which discontinuous crystal grain growth of polycrystalline ferrite occurs and at a temperature higher than the growth start temperature of single-crystal ferrite, A spherical molded body or a spherical sintered body is used as the polycrystalline ferrite, and a single crystal plate having the same crystal structure as the polycrystalline ferrite is used as the single crystal ferrite. 1. A method for producing a single-crystal ferrite sphere, which comprises arranging the spherical molded bodies or spherical sintered bodies so as to make point contact with each other, and growing the spherical molded bodies or spherical sintered bodies into spherical single crystals.